This is true - David himself often goes out. He usually does a pink noise voice-print of the room to see how his speakers interact in situ, then uses it to begin his equalization and timing adjustments (manually is what I recall from the last time I saw him at it). Some of this is done at the speaker (the horizontal timing plates between speaker elements, as well as the back plate resistors - some of these are propagation delay, others are attenuators to do fixed value EQ based on the room) - they also make their own EQ box you can add to the system (especially with their Thor's hammer sub).
Nice speakers... not the best I've ever heard (I've heard Alexandria 2, Maxx, and Sophias), but certainly impressive - all of them.
Every speaker, no matter what design, or cost - interacts differently in every room due to its dimensions, contents and acoustic treatments (or lack thereof). EQ helps mitigate the issues that can arise in each room, to get back to what the speaker designer, and the audio engineers who recorded and mastered the music intended.
If it sounds "better" without the eq - then either the eq is done poorly, or you prefer a sound other than what the recording engineers created. That's cool - but you should recognize that's what it is. Colored sound, not true to the source.
But ultimately - there are many different ways to skin that cat - EQ is one very effective (and relatively cost effective, high quality) way, but not the only way.
Btw, he has the Alexandria xl2s. It wasn't David who came, but two other guys. For the record, he uses almost all analog sources. Reel 2 reel and th clear audio statement table.
Everything colors the sound in home hifi. Everything.